Dried particulate hydrophilic gel as micronutrient delivery system

ABSTRACT

The inclusion of certain organic hydroxy acids, most notably citric acid, in the iron sulfate formulations of at least one prior art hydrophilic polymer delivery system followed by drying and crushing the product into particles has been found to significantly improve the efficiency and ease of application of iron source fertilizer materials for iron-sensitive plants growing on iron-deficient soils for periods exceeding one year. The dried particles most preferably may be selectively metered into soil in or near the seed row as a band application at or prior to planting or spot placed in the root zone of growing plants in soil. The dry band absorbs soil moisture to provide a unique environment which restricts contact of soluble iron fertilizers with the soil and provides for complexation of iron in the formulation with organic hydroxy acids also contained in the formulation, thereby minimizing the extent of chemical reactions with the soil that reduce the availability of the applied iron to plant roots. A unique characteristic of the invention is the maintenance of iron in water soluble plant available form in soil outside the particles or band. Thus, root penetration and proliferation into and around the band also is greater than in the soil matrix, resulting in greater uptake efficiency of applied iron. The ease of precise application to soil, coupled with significantly enhanced crop response and utilization of iron contained in the product, offer considerable advantage over existing iron source fertilizer materials.

The invention herein described may be manufactured and used by or forthe Government for governmental purposes without the payment to us ofany royalty therefor.

This application is a division of application Ser. No. 08/311,228, filedSep. 23,1994, now U.S. Pat. No. 5,632,799.

INTRODUCTION

Chlorosis of plants, which is attributed to iron deficiency, has beenwidely reported in the open literature for well over a century, yetpresently there is no effective, economical method including direct soilapplication to correct such iron deficiencies in plants. Chlorosis ischaracterized by a yellowing of plant leaves due to substantiallydiminished amounts of chlorophyll, the formation of which chlorophyllrequires adequate quantities of the micronutrient iron. Theoretically,such conditions could be quickly corrected by application of, eitherdirectly to the plant or indirectly to the soil at the plant situs, ironsources which are in a form readily available to such plant. Until thepresent time, however, numerous problems have been found to exist withmany iron-containing compounds which tend to prevent their general usefor successfully treating such iron deficiencies in plants. Examples ofsuch problems encountered comprise the cost of the materials, thedifficulty of delivery to a crop, the need and expense for multipleapplications, and the lack of plant response under various soilconditions wherein iron chlorosis occurs.

The materials most commonly utilized to date for effecting treatment,albeit, not totally successful, of iron deficiencies have been ferrousand ferric sulfates and certain organic iron-containing compounds knownas synthetic chelates or natural organic complexes. (John Mortvedt, IronSources and Management Practices for Correcting Iron Chlorosis Problems,Journal of Plant Nutrition 9:961-974, 1986). While the inorganic ferrousand ferric sulfates are relatively inexpensive, plant response to themhas been found to be generally inadequate if they are applied directlyto calcareous soils, wherein most such iron deficiencies occur. Forinstance, it has been long known that subsequent to soil application,iron sulfates quickly react to form compounds such as, for example,ferric hydroxides, the iron values of which are unavailable to plants.While some other sources of iron, generally characterized as chelates,do not react with soil to form unavailable compounds, they are soexpensive that their use is restricted to application on high-valuecrops or for other specialized situations.

Until the present time, the most economical method used to correct ironchlorosis has been multiple and timely foliar applications of ferroussulfate (FeSO₄) to the growing plants. This has been practical only onmoderately iron-deficient soils. Economically justifiable results withsuch periodic foliar application have been poor or are frequently notobtained on soils which are characterized as being very low in availableiron. In addition, the timing of foliar spray applications has beenfound to be quite critical in order to obtain satisfactory correction ofthe chlorosis condition. It has also been observed by researchers andreported in the literature that the leaves of sprayed plants may bedamaged by some foliar sprays containing certain compounds or by sprayscontaining relatively high salt concentrations of other compounds. Inaddition, it has been reported that such foliar application, unlesscontinued periodically over a substantial period of time may not beparticularly effective since new growth appearing after initial sprayingmay again be chlorotic. Accordingly, it may reasonably be concluded thatfoliar spray applications are not always a satisfactory and/oreconomical method for correcting iron deficiencies in plants.

Until the present time, the second most economical method used tocorrect iron chlorosis has been a single soil application of a band ofhydrated hydrophilic polymer (i.e., in the form of a fluid, thixotropicgel, such as commonly seen in certain gel toothpastes) which containsinorganic iron sulfate (Mortvedt, et. al. U.S. Pat. No. 5,221,313, Jun.22, 1993). However, these products are relatively expensive, notconveniently applied to the soil, and require specialized applicationequipment, such as positive displacement pumps, which are not part ofthe normal inventory of farming equipment.

However, it has now been discovered that many of the shortcomings fortreating chlorosis with the invention of Mortvedt, supra, could beovercome by practice of an improvement over said invention. Thisimprovement is an iron delivery system characterized by its ability toeffectively isolate, and provide chemical protection by complexing with,for substantial periods of time, the iron sulfates contained anddelivered therein from the deleterious effects of various soilconstituents which normally give rise to rendering such iron sulfatesunavailable to growing plants. In addition, this improvement is in suchform that allows for soil situs placement with existing, widely used,and commercially available equipment and is less costly per unit of ironand simultaneously more effective in alleviating iron chlorosis inplants than said hydrophilic delivery systems of Mortvedt, supra.Accordingly, the instant invention is presented in a principalembodiment directed to overcoming the chlorosis problem and analternative improved embodiment to hydrophilic polymer micronutrientdelivery systems directed to delivery and focus for more effectiveuptake of iron which is known to be required by growing plants.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the development of inexpensivematerials and means to apply them, which materials are eminentlysuitable for the correction of iron deficiency-induced chlorosis inplants. More particularly, the present invention relates to thedevelopment of certain materials selected from the group of gel-forminghydrophilic polymers, comprising polyacrylamides, cellulose ethers, guargums, propenoate-propenamide, or mixtures thereof, said polymer disposedin combination with citric acid, and the resulting combinations infurther combination with certain iron source materials including, butnot limited to iron sulfates. Still, more particularly, the instantinvention relates to the discovery that certain organic acids,particularly citric acid, if added to the afore-mentioned alreadyhydrated hydrophilic gel-forming polymers or fluid gels of Mortvedt,supra, will significantly increase the efficacy of the hydrated gels incorrecting iron chlorosis of plants. Still, even more particularly, theinstant invention relates to the discovery that certain formulations ofthe hydrated gels which are properly combined with predeterminedproportions of citric acid, and from which is removed sufficientmoisture to result in a friable material from which particulates areeasily recovered can, upon subsequent wetting by water in the soil,react to re-form, in situ, such hydrated gel. The resulting re-formedgel complexes and otherwise protects selected iron compounds to providean economical and readily available iron source imminently suitable forcorrecting iron deficiencies in plant life growing at such situs. On theother hand, it has been found that the same gel formulations, sans saidcitric acid, will not perform in such a desirable manner. Such new andimproved product is herein designated as "dried iron-containing gelparticles;" "dried gel particles;" or more simply "DGP." It has also nowbeen determined that such DGP most preferably should be band applied ina continuous intact band at or prior to planting, or spot placed in theroot zone of growing plants in soil to minimize the contact of theseproducts with the soil so that chemical reactions which adversely affectthe availability of iron in these products to plants are minimized. Whenapplied in such fashion, the DGP will hydrate and coalesce to form acontinuous, intact gel entity, either in the form of a gel band or othersuch isolated gel area, in essentially the same final form as the geldelivery system of Mortvedt, supra, but with considerably enhanced easeof application. Moreover and most significantly, the instant inventionrelates to the discovery that the addition of citric acid to suchcombinations of polyacrylamide polymers and iron-containing materialscauses the formation of a compound or compounds, not previously observedto occur with other hydrophilic polymer/iron source materials, whichwill diffuse out of the hydrated band of DGP into the surrounding soilas evidenced by a diffuse orange-colored zone or "halo", radiatingoutward from the band into the soil. This zone, as evidenced by theorange coloration, likely contains iron in an oxidized, water-solubleform. Incomplete polymerization of acrylic acid during polyacrylamidesynthesis results in free, water-soluble monomers of acrylic acid withinthe polymer structure. It is speculated that these monomers react withcitric acid and iron to form a cyclic, water-soluble iron complex whichdiffuses from the gel band into the soil. The bonding strength of thecomplex for iron is sufficient to prevent soil reactions which result inprecipitation of iron as compounds which are unavailable to plants. Theacrylic acid alone will not form a sufficiently strong complex with ironto prevent these reactions (log K°=4.2 for Fe(II)acrylate). Moreover,and still more significantly, observation of the soil matrix in whichthis orange-colored zone or halo occurs, clearly shows an unusualpropensity of root and root hair growth in the region where DGP wasapplied, in preference to the surrounding soil matrix. Such rootproliferation typically occurs in zones of enhanced fertility in soils,and in such instances where DGP has been applied such enhancement islikely due to a greater concentration of available iron in this zonethan in the surrounding soil. This enhanced and concentrated region ofroot growth occurred to a much lesser extent in like polymer systemswhich contained iron, but not citric acid, and did not occur at all wheniron and citric acid were omitted from otherwise similar formulations.

Furthermore, it has now been discovered that oftentimes the DGP willabsorb up to 100 times its own weight in water from contact with moistsoil. This process results in swelling of the DGP such that veins orislands of micronutrient-enriched hydrogel are established along withconcomitant displacement of the soil around the DGP which results in azone more easily penetrated and expanded into by plant roots than is anormal soil matrix and which by virtue of copious amounts of water ofhydration available to roots growing therein, as well as the abundantsupply of micronutrients, provides a region where root growth issubstantially enhanced.

In addition, it has now been demonstrated in field testing that such DGPis in a form which may be easily, selectively, and precisely dispensedinto soil as a sub-surface band of dry particles by means of a deviceknown in the trade as a pesticide applicator box. This device isdesigned to contain only small amounts of pesticides, as compared toequipment used for application of major plant nutrients, or"macronutrients", such as nitrogen (N), phosphorus (P), and potassium(K), since such pesticides are normally applied to soil in small amounts(on the order of 1 to 5 pounds per acre, much as with applications ofiron) and thus precise metering of the material is required. Thisprecise metering consideration is most important because iron chlorosisresulting from iron deficiencies in soil has been found to occur inseparate or isolated areas within any of a number of given fields, whichareas range from less than one, up to several acres in dimension, whichare oftentimes isolated one from another and which produce little, ifany, gainful yield. Unfortunately, currently practiced commercialpractices for planting such high pH, calcareous and iron-deficientfields, wherein macronutrients, which are required in large amounts byplants are routinely applied to such areas in a blanket application, donot provide a means which is practical to selectively dispense thesemicronutrients only in such isolated areas. However, in the practice ofthe instant invention, if the locations of these iron-deficient areasare known by previous experience, or are otherwise effectively mapped,the DGP can be selectively applied during application of themacronutrients by using a variable rate pesticide applicator boxequipped with a banding attachment for subsurface banding of DGP onlyupon reaching such susceptible areas and not across the whole area ofthe field. Thus, gainful yields may be realized from areas where beforelittle or none were possible and the added expense of the DGP istherefore more than offset by the increased economic return of suchyields.

2. Description of the Prior Art

Iron is an essential element in plant nutrition and generally isclassified as a micronutrient. It is known to be involved in thesynthesis of chlorophyll which in turn is required for photosynthesis inplants. A deficiency of this micronutrient in growing plants, which canbe greatly exaggerated in calcareous type soils, is oftentimes the causeof chlorosis, which is characterized by a yellowing of plant leaves andstems and which results in particularly poor growth.

Currently available practices for alleviating such iron deficiencies ingrowing plants include the application of synthetic iron chelates tosoil or the use of various soluble iron compounds as foliar sprays fordirect application to the plants or the use of certain hydrophilicpolymer delivery systems. Currently, the least expensive, in terms ofup-front per unit cost, water-soluble iron compound in use is ironsulfate, either in its reduced state, e.g., (FeSO₄) or in the ferricstate, e.g. Fe₂ (SO₄)₃ !. However, neither form supra, of iron sulfateshould be applied directly to soil lest either source quickly becomescombined with certain components in the soil to form water-insolublecompounds thereby rendering such iron unavailable to growing plants.

The synthetic chelate, FeEDDHA ferric chelate of ethylenediamine(di-(o-hydroxyphenyl acetate))!, has long been considered by manyskilled in the art to be the most effective iron fertilizer for soilapplication, especially in calcareous soils (Arthur Wallace, A Decade ofSynthetic Chelating Agents in Inorganic Plant Nutrition, EdwardsBrothers, Inc., Ann Arbor, Mich., 1962). However, the per unit cost ofiron in FeEDDHA is quite high, which makes this iron chelate materialmuch too expensive for application to relatively low-value field crops.Another currently available and somewhat less expensive iron chelatematerial, FeEDTA (monosodium ferric ethylenediamine tetraacetate), hasproven to be effective for crops growing in near neutral soils but notin calcareous, high-pH soils wherein most iron deficiencies occur.Another recent discovery also somewhat less costly than chelates, arehydrophilic polymer delivery systems (Mortvedt, supra). However,application of the materials of Mortvedt, is difficult and requiresspecialized equipment and the polymer in the formulations is alsorelatively expensive. Nevertheless, the initial per unit cost of iron issignificantly lower than in the chelates. Accordingly, it should bereadily apparent that iron sulfate would be the most economical andeminently suitable iron source material for use on field crops if itonly remained available to growing plants subsequent to its contact orjuxtapositioning with the soil situs. Therefore, additives or conditionswhich can significantly improve the effectiveness of iron sulfateintended for the treatment of chlorosis could, in turn, result in aneconomically effective iron source for soil application.

Currently, it is the practice in the trade for iron source material tobe applied to soil separately or to be incorporated with other materialsin the processing or blending of fertilizers or to be applied in ahydrophilic gel polymer matrix. The effectiveness of iron sourcematerials in maintaining a supply of iron to growing plants depends uponthe chemical nature of such iron source materials and/or the soil, aswell as rate and/or frequency of their application. Economicconsiderations regarding the use of iron source materials are determinedby costs and rate of their application as well as the ease ofapplication relative to the returns attributable to increased yields ofthe crops to which they are applied. Presently, the most effective ironchelate, FeEDDHA, is so costly that its use is restricted to high-cashvalue crops such as, for example, apples, grapes, and peaches, orhigh-cash value ornamental crops such as, for example, rhododendrons,azaleas, and dwarf citrus, while other methods, i.e., fluid hydrophilicpolymer delivery systems, are nonetheless still expensive in addition tobeing difficult to apply and are not as effective as FeEDDHA. The leastcostly, on a front-end per unit cost basis, iron source materials areineffective when used in procedures designed to correct iron chlorosisin many lower value field crops, such as, for example, corn, grainsorghum and soybean, which nonetheless are planted in large acreage andconstitute the major portion of modern production agriculture.

From the aforesaid, it should now be abundantly clear that the prior artmaterials designed as, or intended to be, iron sources are too costly upfront to be economical for use on most field crops or are difficult toapply and require specialized application equipment, or althoughavailable at relatively low unit cost, are still highly uneconomical touse since they are ineffective in maintaining a supply of available ironto crops growing on iron-deficient soils.

SUMMARY OF THE INVENTION

It has now been discovered that significant improvements have been madeto the invention of Mortvedt, supra. These improvements include 1) theaddition of citric acid (or other similar organic acids within the samechemical family, known as "hydroxy acids", such as lactic acid, malicacid, or tartaric acid, etc.) to the hydrophilic polymer deliverysystems of Mortvedt, supra, to significantly and greatly increase theefficacy of said delivery system in alleviating iron deficiency-inducedchlorosis in plants grown on calcareous, high pH soil; 2) formulatingthe polymer delivery materials of Mortvedt, supra, to include citricacid or other organic acid of the same chemical family, thereafterdrying and crushing the resulting material to a relatively uniformparticle size to significantly and greatly facilitate ease of packaging,handling and application to soil, whether in band or spot application,with significant increase in efficiency in alleviating iron chlorosis inplants; accordingly, the application of this material in relativelynarrow continuous bands, on the order of about 1/4 to 3/4 inches indiameter, along or parallel to the seed row or spot placed in the rootzone of living plants is normally the easiest and most convenient mannerof distribution; and 3) cellulose ethers, plant-derived guar gums, andpropenoate-propenamides, which are all different chemical classes ofhydrophilic polymers, and which were previously shown by Mortvedt,supra, to be mediocre for use in hydrophilic polymer delivery systems,may now be used with as good and essentially equal effectiveness as themore costly polyacrylamide or polyacrylamide-polyacrylate polymers ascarriers of iron in DGP formulations.

It would appear that the principal mechanisms which are responsible forpreserving, for a substantial period of time, these iron sourcematerials in formulations of DGP in a form which ultimately is readilyavailable to growing plants is one of isolation by chemical means ofcomplexing with citric acid, and by physical means afforded by thehydrated gel matrix, of such iron source materials from the deleteriouseffects of or combinations with soil components, including aqueousmedia, at or near the application situs. In addition, it has now beendiscovered that the most preferred methods of application of such citricacid-containing DGP, namely, subsurface band application to soil at orprior to planting or spot application in the root zone of growing plantsin soil, will result in the formation of a hydrated continuous gel bandwhen exposed to moisture in the soil, thus isolating such materials fromreacting with the soil to form compounds which are unavailable toplants. Furthermore, observation of citric acid-containing DGP in situin soil revealed the formation of a diffusion zone of iron from the gelband into the surrounding soil, such iron being in forms protected fromsoil reactions, which thus substantially increased plant utilization ofthe iron contained in the formulations over the same products which donot contain citric acid.

Results of greenhouse investigations indicated that these driedformulations of iron sources, citric acid, and hydrophilic polymercombinations are effective for use on a variety of iron-sensitive cropsgrowing in iron-deficient soils. It has also been discovered that theymay be band applied near the seed row at planting. In addition, it isproposed that they may be used as specialty fertilizers to other crops,providing they are spot placed in the root zone or what will be the rootzone in the soil rather than on or juxtaposed the soil surface. Thesecombinations may be especially beneficial for certain slower growingperennial crops such as fruit trees, grape vines, and shrubs becausebiodegradation of the mixture buried within soil occurs slowly over along period of time. Iron in the formulations is thus protected fromreactions with soil and maintained in a form available to these plantsduring periods of active growth and of active iron uptake as well asduring slower growth periods when demand for iron is low. Thesecombinations may also be especially beneficial to lower-cash value rowcrops such as grain sorghum, corn, and soybeans since the product isless costly to produce and use than alternative methods of ironfertilization and also provides for sustained iron availability for suchfield crops during an entire growing season, or longer. One DGP producedaccording to the practice of the instant invention recently has beenfield tested for corn growing on high pH, calcareous soil in Nebraska,where iron deficiencies typically occur. Photographic documentation ofplant vigor and growth substantiated the effectiveness of the DGP as asuperior iron source for the plants during early growth stages,throughout the season until crop maturity, and for a subsequent corncrop planted one year later. Further elaboration of this test is givenwithin the Examples, infra.

Investigations into the utilization of iron in the DGP revealed thatband application established veins of the DGP in the immediate vicinityanticipated for plant root development. These bands of dry materialsubsequently were hydrated by moisture in the soil to form continuous,intact gel bands, in exactly the same physical form as the fluid gels ofMortvedt, supra. After sufficient time had elapsed for such development,cross sectioning of such veins and observing the soil matrix surroundingsame clearly showed an unusual propensity of root and root hair growthin the product region in preference to the surrounding soil matrix. Inaddition, the development of an orange-colored zone or "halo" in thesoil around the product was suggestive of iron transport in soluble formaway from the gel band, thereby increasing the volume of iron-enrichedsoil available for root exploration with resultant significantlyincreased efficiency of iron uptake by the plant. This clearlyestablished that the instant new and novel delivery system focuses plantroot development in a fashion whereby contact with and uptake of iron insuch veined regions is not only substantially enhanced but is, indeed,totally optimized.

Another aspect of the instant invention relates to a method of enhancingthe yield and/or growth of plants by distributing the composition ofthis invention in the "plant growth media" in which the plants are beinggrown within reach of the root system of the plants (hereinafterreferred to as "root zone"). As used herein, the term "plant growthmedia" refers to various natural and artificial media which supportplant growth, including but not limited to soil, potting mixtures oforganic and inorganic matter, and artificial media such as vermiculiteor polyurethane foam.

Yet another aspect of the present invention relates to a method forinhibiting the degradation of certain water-soluble iron sourcemicronutrient materials, principally iron sulfates, including ferricsulfate or ferrous sulfate or both, when said iron source micronutrientsare applied to such plant growth media, which aspect comprises providingan effective isolation of said water-soluble iron source micronutrientsfrom said plant growth media such that same do not react with componentstherein in a fashion whereby the iron sulfates form water-insoluble orsubstantially water-insoluble compounds, which water-insoluble compoundsare or become unavailable to plant growth sought to be treated with suchiron source micronutrients. A principal embodiment of this invention,which provides such effective isolation is the homogeneous mixing andresultant chemical interaction between the polymer, citric acid and ironsources in the DGP from which arises complexation and protection of ironsulfates from soil reactions by citric acid, and physical isolation andcontainment of iron by the gel matrix from soil reactions which wouldotherwise render iron unavailable to plants. Practice of the instantinvention ensures that iron sulfates so processed remain substantiallywater-soluble in the resulting formed mixture.

As used herein, the term "effective isolation" refers to the protectivemechanism of isolation and containment by a gel matrix and complexationof the iron sulfates, supra, in an intimate mixture formed with citricacid or other such organic acid and iron sulfate that encompasses anisolation or separation so effective that all or most of the so-treatediron sulfates remain substantially water-soluble for at least a periodof about 2 weeks and preferably a period ranging from at least about 4to about 6 weeks, more preferably at least about 120 days, and mostpreferably for a period of time ranging upwards to 1 year, or more.

As used herein, the terms "dried iron-gel particles," "dried gelparticles," or more simply, "DGP" refer to the product resulting frommixing of predetermined amounts of iron source, effective amounts ofcitric acid or other similar organic acid and a hydrophilic polymer intoa fluid gel which is then dried and crushed into appropriately sizedparticles for ease of application. The effective amount of citric acidfor use in the DGP formulations was calculated mathematically by use ofa procedure known in the trade as "mole fraction calculations," whichcalculations determine the concentration of a ligand (citric acid) thatwill complex with a given concentration of metal (iron), or vice-versa,up to a maximum amount where equilibria between the two is reached andno further complexation will occur. As an example, given a 5 percentsolution of iron sulfate, containing 1 percent iron, the effectiveconcentration of citric acid was mathematically determined to be 10percent.

As used herein, the term "substantially water-soluble" encompassesmaterials which are initially water-soluble such as ferric sulfate ormaterials which have only degraded, by reaction with components ingrowth media to the point that the resulting reaction products incombination with the unreacted materials, in the aggregate, provide amaterial which is at least about 60 percent water-soluble.

As used herein, the term "root zone" refers to that area in the plantgrowth media within the reach of the root system of a particular desiredplant or crop and in the field normally comprises that portion of thesoil matrix generally beneath the seed planting band and areasjuxtaposed thereto, generally parallel with the band and protrudingdownwardly from a few inches to perhaps about a foot. In the practice ofthe invention there will oftentimes be provided veins or islands ofiron-enriched DGP through such root zone in a fashion such that anyplant roots entering therein will be provided with an environmentenhanced both mechanically and nutritionally by virtue of the uniformityof consistency of said mixture which is considerably more easilypenetrated and expanded into than is a normal soil matrix and which byvirtue of the ease of wetting of the mixture for the roots growingtherein, as well as the abundant supply of desirable iron within themixture and in an iron rich diffusion zone immediately outside themixture and extending perhaps 4 up to 7 centimeters into the soil awayfrom the mixture band, provides a micro-environment wherein root growthis substantially enhanced.

As used herein, the term "enhanced root growth region" refers to suchplant growth media discontinuities comprising iron-enriched DGP mixturesand the associated diffusion zone of the type herein contemplated andreferenced.

As used herein and applied to the resulting dried hydrogel, the term"friable" refers to a physical characteristic whereby the normallyresilient or tacky hydrogel has sufficient water removed therefrom toconvert it into a relatively hard, brittle friable material, wherebyordinary crushing means and methods including roller crushers or thelike are easily comminuted.

Still yet another aspect of the instant invention relates to the ease ofapplication to soil. The physical properties (dry, granular, andfree-flowing) of the DGP product render it eminently more suitable forstate of the art variable rate technology in modern agriculturalapplicator equipment, which enables soil application rates to be madeselectively, precisely, and accurately, and thus, economically, topredetermined areas, and only to those areas, if so desired, within afield. Thus, crop yields may be obtained in areas, such as, for example,high pH, calcareous regions within a field which previously had nohistory of gainful yields.

OBJECTS OF THE INVENTION

It is therefore a principal object of the present invention to provide anew and improved combination of materials which are eminently suitablefor supplying iron to soil systems and/or to the situs of growing plantsfor substantial periods of time of at least about 28 days, preferably ofat least about 60 days, and most preferably of at least about 120 daysor longer, and in a form such that they can readily be absorbed by theroots of such growing plants.

Another principal object of the present invention is to provide a newand improved method, as well as a new combination of materials eminentlysuitable for supplying iron to soil systems and/or to the situs ofgrowing plants for substantial periods of time and in a form such that,although such materials most preferably may be band applied near theseed row in soil or spot placed directly in the root zone of growingplants, they will be readily available for absorption by the roots ofsuch growing plants.

Still another principal object of the present invention is to provide anew and improved method, as well as an improved combination of materialseminently suitable for soil applications and for supplying iron to soilsystems and/or to the situs of growing plants in a form such that willbe absorbed by the roots of such growing plants and wherein suchmaterials comprise either separate components or admixtures ofcomponents including hydrophilic polymers of various chemical classes,certain organic acids, particularly citric acid, and iron sourcematerials, said iron source materials including ferrous and ferricsulfate.

A further principal object of the present invention is to provide a newand improved method, as well as a new combination of materials eminentlysuitable for supplying iron to soil systems and/or to the situs ofgrowing plants to act as a most efficient delivery system for such iron,and for uptake by growing plants in a manner wherein upon contact andpenetration of said DGP, the plant roots evidence an unusual propensityfor further growth thereinto, and into a defined diffusion zone of aplant nutrient, whereby the uptake of iron values are more effectivelyutilized than if iron were homogeneously mixed in the surrounding soilmatrix.

Still a further principal object of the present invention in a principalembodiment thereof is to provide new procedures to effect the mixing ofcertain gel-forming polymers with aqueous citric acid-containing andaqueous iron-containing solutions to result in the formation of gelswhich can be dried and subsequently be broken into particles which canbe more easily applied to soil situses than fluid gels to providethereat sufficient available iron as may be required by growing plants.

Still further and more general objects and advantages of the presentinvention will appear from the more detailed description set forth inthe following disclosure and examples, it being understood, however,that this more detailed description is given by way of illustration andexplanation only and not necessarily by way of limitation, since variouschanges therein may be made by those skilled in the art withoutdeparting from the true spirit and scope of the gist underlying thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is directed to methods of mixing, as well as thespecific compositions utilized therein for applying to a designated soilsitus, various combinations of hydrophilic polymer, citric acid, andselected water-soluble compounds of iron including, in the mostpreferred embodiments, ferrous sulfate, or ferric sulfate. Practice ofthe instant invention results in the formation of new compounds forimproved fertilizers having incorporated therein water-soluble compoundsof iron in forms wherein same are sufficiently isolated, both chemicallyand physically, at least temporarily, from contact with soil media butare juxtaposed such media such that the iron values therein remainavailable to maintain the prerequisite supply of iron in a form readilyuseful to plants growing at or near such situs.

The combinations of hydrophilic polymer, citric acid, and iron sulfatewere analyzed with a Nicolet 60SX Fourier transformed infraredspectroscopy (FTIR) system before hydration with deionized water, andafter hydration and drying, to confirm the formation of new compounds.Each sample material was pelletized with KBr for analysis; the spectrumfrom a KBr pellet, used as a background blank, was subtracted from eachinitial sample spectrum.

Referring now generally to Table I-a through Table V-b, there are shownby peak number (for convenience) the infrared spectral peak positions,intensities, and relative intensities for various individual compositemixtures of a hydrophilic polymer, citric acid, and iron sulfate. Atable designated with the letter "a" shows the infrared absorption datafor a given mixture before hydration and drying; the counterpart tabledesignated with the letter "b" shows the data for the mixture afterhydration and drying, i.e., the dried gel, or DGP. The peaks that werepresent in the spectra, and which are designated by peak number and peakposition in Table I-a through Table V-b, represent the frequencies ofvibrational bending and stretching that occurred within the molecules ofthe compounds due to the absorbance of light energy. Shifts in suchvibrational frequencies in the region where light was absorbed (due topeak splitting, additions or deletions, or a change in the relativeintensity of an existing peak) were indicative of changes in chemicalbonding within the mixtures after hydration and drying. Such changes inbonding consistently occurred, regardless of the polymer type, and thusresulted in the formation of new compounds which were notably, if notentirely, different from those present in the original, unhydratedmixtures. For example, an unhydrated mixture containing a polyacrylamidepolymer, iron sulfate, and citric acid was spectrally similar to ananalogous mixture containing a polyacrylate due to the closesimilarities in the chain backbone structure. Although each mixtureshared many of the same spectral traits after hydration and drying, eachalso exhibited such changes as to be not only different from each other,but also different in form from the original mixture.

Referring now specifically to Table I-a and Table I-b, therein are shownthe infrared data for a mixture of a polyacrylamide polymer, citricacid, and iron sulfate, said mixture either unhydrated or previouslyhydrated and then dried. Significant differences are noted between theabsorption spectra for the unhydrated mixture (Table I-a) and for thehydrated and dried mixture (Table I-b). Twenty absorption peaks wereidentified in the unhydrated mixture versus 29 peaks in the dried gel.There were 10 absorption peaks common to both spectra (peak matches).Splitting and/or addition of peaks occurred with the dried gel in theregions 2600-4000, 1500-2000, and 650-500 cm⁻¹. Changes in the relativeintensity and magnitude of peaks common to both spectra were alsoapparent. The major changes in the region 2600-4000 cm⁻¹ were thesplitting of peak number 1 (Table 1-a) into two peaks occurring atwavenumbers 3481 and 3400 (peak numbers 1 and 2, Table 1-b) and theaddition of peak numbers 3 and 5 (Table 1-b). Peak number 6 (Table 1-b)did not occur in the unhydrated mixture. Three additional peaks occurredin the region 1500-2000 cm⁻¹ with the hydrated and dried gel mixture(peak numbers 9, 10, and 11, Table 1-b). Eight additional peaks occurredin the region 650-1500 cm⁻¹ with the hydrated mixture (peak numbers 12,14, 15, 16, 18, 19, 21, and 25, Table 1-b). There was no discerniblepattern to changes in magnitude and relative intensity of the sevenpeaks in this region common to both the unhydrated mixture and thehydrated and dried mixture.

                  TABLE I-a                                                       ______________________________________                                        Infrared Absorption Bands Frequency (cm.sup.-1) for a Composite               Mixture of DGP (Iron Sulfate, a Polyacrylamide Polymer,                       and Citric Acid) Before Hydration and Drying                                  Peak    Peak         Peak     Relative                                        No.     Position     Intensity                                                                              Intensity                                       ______________________________________                                        1       3429         S-B      8                                               2       3275         Sh       7                                               3       3018         Sh       6                                               *4      2625         W-B      3                                               5       2565         Sh       3                                               6       1981         VW-B     1                                               *7      1726         S-Sp     9                                               8       1628         M-Sp     4                                               *9      1398         M-Sp     4                                               10      1338         W-B      3                                               *11     1221         MS-Sp    6                                               12      1134         Sh       5                                               *13     1115         M-Sp     5                                               14      1088         Sh       4                                               *15     987          VW-Sp    2                                               *16     937          VW-Sp    2                                               *17     897          VW-Sp    2                                               *18     791          W-Sp     2                                               *19     606          M-Sp     4                                               20      507          Sh       4                                               ______________________________________                                         Sh = shoulder;                                                                B = broad;                                                                    Sp = sharp;                                                                   S = strong;                                                                   MS = medium strong;                                                           M = medium;                                                                   W = weak;                                                                     VW = very weak.                                                               Relative intensities are on a scale of 1 to 10.                               *Peaks that occurred in mixtures both before and after hydration are          indicated with an asterisk.                                              

                  TABLE I-b                                                       ______________________________________                                        Infrared Absorption Bands Frequency (cm.sup.-1) for a Composite               Mixture of DGP (Iron Sulfate, a Polyacrylamide Polymer,                       and Citric Acid) After Hydration and Drying                                   Peak    Peak         Peak     Relative                                        No.     Position     Intensity                                                                              Intensity                                       ______________________________________                                        1       3481         MS-Sp    4                                               2       3400         MS-Sp    4                                               3       3215         MS-B     4                                               4       2937         Sh       3                                               5       2700         Sh       2                                               *6      2621         W-B      2                                               7       2540         W-B      2                                               *8      1730         S-Sp     5                                               9       1659         Ms-Sp    4                                               10      1610         S-Sp     4                                               11      1566         Sh       4                                               12      1419         Ms-Sp    4                                               *13     1396         S-Sp     4                                               14      1377         Sh       4                                               15      1325         MS-Sp    3                                               16      1286         Ms-Sp    3                                               *17     1225         Ms-Sp    4                                               18      1194         MS-Sp    4                                               19      1142         S-Sp     4                                               *20     1109         S-Sp     4                                               21      1074         MS-Sp    4                                               *22     978          Sh       3                                               *23     937          W-Sp     2                                               *24     891          M-Sp     3                                               25      850          M-Sp     3                                               *26     795          M-Sp     3                                               *27     613          Ms-Sp    4                                               28      580          Ms-Sp    4                                               29      540          Sh       4                                               ______________________________________                                         Sh = shoulder;                                                                B = broad;                                                                    Sp = sharp;                                                                   S = strong;                                                                   MS = medium strong;                                                           M = medium;                                                                   W = weak;                                                                     VW = very weak.                                                               Relative intensities are on a scale of 1 to 10.                               *Peaks that occurred in mixtures both before and after hydration are          indicated with an asterisk.                                              

Referring now specifically to Table II-a and Table II-b, therein areshown the infrared data for a mixture of a guar gum polymer, citricacid, and iron sulfate, either unhydrated or previously hydrated anddried. Significant differences are noted between the absorption spectrafor the unhydrated mixture (Table II-a) and for the hydrated and driedmixture (Table II-b). Thirty-six absorption peaks were identified in theunhydrated mixture versus 20 peaks in the dried gel. There were eightabsorption peaks common to both spectra (peak matches). The majorchanges noted in the spectrum for the dried gel were the loss of fourpeaks in the region 2600-4000 cm⁻¹, the loss of one peak in the region1500-2000 cm⁻¹, and the loss of twelve peaks in the region 500-1500cm⁻¹. There were also minor changes in the intensity and magnitude ofpeaks common to both spectra.

                  TABLE II-a                                                      ______________________________________                                        Infrared Aosorption Bands Frequency (cm.sup.-1) for a Composite               Mixture of DGP (Iron Sulfate, a Guar Gum Polymer, and                         Citric Acid) Before Hydration and Drying                                      Peak    Peak         Peak     Relative                                        No.     Position     Intensity                                                                              Intensity                                       ______________________________________                                        1       3495         S-Sp     8                                               2       3454         S-Sp     7                                               3       3383         S-Sp     6                                               4       3292         S-Sp     3                                               *5      2943         Sh       3                                               6       2640         W-B      1                                               7       2563         VW-B     9                                               *8      1998         VW-B     4                                               9       1743         S-Sp     4                                               10      1714         S-Sp     3                                               *11     1626         W-Sp     6                                               12      1416         W-Sp     5                                               13      1392         M-Sp     5                                               14      1360         W-Sp     4                                               15      1340         W-SP     2                                               16      1321         W-Sp     2                                               17      1308         W-Sp     2                                               18      1292         W-Sp     2                                               19      1240         M-Sp     4                                               20      1217         MS-Sp    5                                               21      1198         Ms-Sp    4                                               22      1176         Ms-Sp    5                                               23      1144         Ms-Sp    5                                               24      1113         Ms-Sp    5                                               *25     1082         Ms-Sp    4                                               26      989          Sh       2                                               *27     941          VW-Sp    2                                               *28     904          VW-Sp    1                                               *29     881          VW-Sp    1                                               30      818          VW-Sp    2                                               31      783          W-Sp     2                                               32      685          Sh       2                                               33      638          Sh       3                                               *34     600          M-Sp     3                                               35      546          W-Sp     3                                               36      498          W-Sp     3                                               ______________________________________                                         Sh = shoulder;                                                                B = broad;                                                                    Sp = sharp;                                                                   S = strong;                                                                   MS = medium strong;                                                           M = medium;                                                                   W = weak;                                                                     VW = very weak.                                                               Relative intensities are on a scale of 1 to 10.                               *Peaks that occurred in mixtures both before and after hydration are          indicated with an asterisk.                                              

                  TABLE II-b                                                      ______________________________________                                        Infrared Absorption Bands Frequency (cm.sup.-1) for a Composite               Mixture of DGP (Iron Sulfate, a Guar Gum Polymer, and                         Citric Acid) After Hydration and Drying                                       Peak    Peak         Peak     Relative                                        No.     Position     Intensity                                                                              Intensity                                       ______________________________________                                        1       3388         S-B      8                                               *2      2941         Sh       5                                               3       2629         W-B      2                                               *4      1992         VW-B     1                                               5       1732         S-Sp     8                                               *6      1633         W-Sp     2                                               7       1400         M-Sp     4                                               8       1194         S-Sp     7                                               9       1138         Ms-Sp    6                                               *10     1082         MS-Sp    6                                               11      1018         Sh       4                                               12      976          Sh       2                                               *13     941          Sh       2                                               *14     897          VW-Sp    2                                               *15     874          VW-Sp    2                                               16      812          W-Sp     3                                               17      665          W-Sp     2                                               18      623          W-Sp     3                                               *18     602          W-Sp     3                                               19      525          W-Sp     3                                               ______________________________________                                         Sh = shoulder;                                                                B = broad;                                                                    Sp = sharp;                                                                   S = strong;                                                                   MS = medium strong;                                                           M = medium;                                                                   W = weak;                                                                     VW = very weak.                                                               Relative intensities are on a scale of 1 to 10.                               *Peaks that occurred in mixtures both before and after hydration are          indicated with an asterisk.                                              

Referring now to Table III-a and Table III-b, therein are shown theinfrared data for a mixture of a polyacrylate polymer, citric acid, andiron sulfate, either unhydrated or previously hydrated and dried.Significant differences are noted between the absorption spectra for theunhydrated mixture (Table III-a) and for the hydrated and dried mixture(Table III-b). Eighteen absorption peaks were identified in theunhydrated mixture versus 35 peaks in the dried gel. There were 12absorption peaks common to both spectra (peak matches). Splitting and/oraddition of peaks occurred with the dried gel in the regions 2600-4000,1500-2000, and 1000-1500 cm⁻¹. The majority of splitting and/oradditions occurred in the region 1000-1500 cm⁻¹. The only clearincreases in relative intensity of peaks common to both spectra occurredat peak numbers 9, 21, and 22 (Table III-b) with the hydrated and driedgel mixture.

                  TABLE III-a                                                     ______________________________________                                        Infrared Aosorption Bands Frequency (cm.sup.-1) for a Composite               Mixture of DGP (Iron Sulfate, a Polyacrylate Polymer,                         and Citric Acid) Before Hydration and Drying                                  Peak    Peak         Peak     Relative                                        No.     Position     Intensity                                                                              Intensity                                       ______________________________________                                        1       3429         S-B      8                                               2       3250         Sh       7                                               3       2953         Sh       5                                               *4      2600         W-B      3                                               *5      1986         VW-B     1                                               *6      1728         S-Sp     8                                               *7      1630         M-Sp     4                                               8       1514         Sh       1                                               *9      1400         W-Sp     4                                               10      1350         Sh       3                                               *11     1221         M-Sp     5                                               *12     1144         M-Sp     4                                               *13     1105         M-Sp     4                                               *14     982          VW-Sp    2                                               *15     937          VW-Sp    2                                               *16     893          VW-Sp    2                                               *17     793          VW-Sp    2                                               18      609          W-SP     4                                               ______________________________________                                         Sh = shoulder;                                                                B = broad;                                                                    Sp = sharp;                                                                   S = strong;                                                                   MS = medium strong;                                                           M = medium;                                                                   W = weak;                                                                     VW = very weak.                                                               Relative intensities are on a scale of 1 to 10.                               *Peaks that occurred in mixtures both before and after hydration are          indicated with an asterisk.                                              

                  TABLE III-b                                                     ______________________________________                                        Infrared Absorption Bands Frequency (cm.sup.-1) for a Composite               Mixture of DGP (Iron Sulfate, a Polyacrylate Polymer,                         and Citric Acid) After Hydration and Drying                                   Peak    Peak         Peak     Relative                                        No.     Position     Intensity                                                                              Intensity                                       ______________________________________                                        1       3479         MS-Sp    7                                               2       3398         S-Sp     8                                               3       3242         Sh       6                                               4       2976         Sh       5                                               *5      2619         W-Bp     3                                               6       2542         Sh       3                                               *7      1981         Vw-B     1                                               *8      1728         S-Sp     9                                               *9      1610         M-Sp     6                                               10      1564         W-Sp     4                                               11      1554         W-Sp     4                                               12      1502         Sh       2                                               13      1479         Sh       2                                               14      1419         M-Sp     5                                               *15     1396         M-Sp     5                                               16      1375         Sh       4                                               17      1325         W-SP     4                                               18      1286         M-Sp     4                                               *19     1230         M-Sp     5                                               20      1194         M-Sp     5                                               *21     1144         M-Sp     6                                               *22     1103         M-Sp     6                                               23      1072         M-Sp     4                                               *24     982          VW-Sp    2                                               *25     939          VW-Sp    2                                               *26     893          VW-Sp    2                                               *27     876          Sh       2                                               28      850          VW-Sp    2                                               29      795          W-Sp     3                                               30      700          Sh       3                                               31      669          Sh       3                                               32      617          W-Sp     4                                               33      580          W-Sp     4                                               34      563          Sh       4                                               35      540          W-Sp     4                                               ______________________________________                                         Sh = shoulder;                                                                B = broad;                                                                    Sp = sharp;                                                                   S = strong;                                                                   MS = medium strong;                                                           M = medium;                                                                   W = weak;                                                                     VW= very weak.                                                                Relative intensities are on a scale of 1 to 10.                               *Peaks that occurred in mixtures both before and after hydration are          indicated with an asterisk.                                              

Referring now to Table IV-a and Table IV-b, therein are shown theinfrared data for a mixture of a cellulose ether polymer, citric acid,and iron sulfate, either unhydrated or previously hydrated and dried.Slight, but significant differences are noted between the absorptionspectra for the unhydrated mixture (Table IV-a) and for the hydrated anddried mixture (Table IV-b). Seventeen absorption peaks were identifiedin the unhydrated mixture and in the dried gel. There were 14 absorptionpeaks common to both spectra (peak matches). A clear increase in therelative intensity/resolution of peaks 7, 8, 10, 11, and 12, and asignificant shift in wavenumber location of peaks 10 and 11 were themajor distinguishing differences noted in the spectrum of the dried gelmaterial.

                  TABLE IV-a                                                      ______________________________________                                        Infrared Absorption Bands Frequency (cm.sup.-1) for a Composite               Mixture of DGP (Iron Sulfate, a Cellulose Ether, Polymer,                     and Citric Acid) Before Hydration and Drying                                  Peak    Peak         Peak     Relative                                        No.     Position     Intensity                                                                              Intensity                                       ______________________________________                                        *1      3417         S-B      6                                               *2      2941         Sh       4                                               *3      2627         W-B      2                                               *4      2023         VW-B     1                                               *5      1728         S-Sp     5                                               *6      1632         W-Sp     2                                               *7      1385         M-Sp     3                                               *8      1358         Sh       2                                               9       1327         Sh       2                                               10      1225         M-Sp     3                                               11      1113         M-Sp     3                                               12      1061         M-Sp     3                                               *13     937          VW-Sp    1                                               *14     887          VW-sp    1                                               *15     791          VW-Sp    1                                               *16     598          W-Sp     2                                               17      503          Sh       2                                               ______________________________________                                         Sh = shoulder;                                                                B = broad;                                                                    Sp = sharp;                                                                   S = strong;                                                                   MS = medium strong;                                                           M = medium;                                                                   W = weak;                                                                     VW = very weak.                                                               Relative intensities are on a scale of 1 to 10.                               *Peaks that occurred in mixtures both before and after hydration are          indicated with an asterisk.                                              

                  TABLE IV-b                                                      ______________________________________                                        Infrared Absorption Bands Frequency (cm.sup.-1) for a Composite               Mixture of DGP (Iron Sulfate, a Cellulose Ether, Polymer,                     and Citric Acid) After Hydration and Drying                                   Peak    Peak         Peak     Relative                                        No.     Position     Intensity                                                                              Intensity                                       ______________________________________                                        *1      3423         S-B      7                                               *2      2941         M-B      4                                               *3      2621         VW-B     2                                               *4      2010         VW-B     1                                               *5      1728         S-Sp     7                                               *6      1632         W-Sp     3                                               *7      1390         W-Sp     3                                               *8      1350         W-Sp     3                                               9       1298         W-Sp     3                                               10      1205         MS-Sp    6                                               11      1126         MS-Sp    5                                               12      1078         MS-Sp    5                                               *13     945          Sh       2                                               *14     883          VW-B     1                                               *15     796          W-B      2                                               *16     602          M-Sp     3                                               17      523          Sh       3                                               ______________________________________                                         Sh = shoulder;                                                                B = broad;                                                                    Sp = sharp;                                                                   S = strong;                                                                   MS = medium strong;                                                           M = medium;                                                                   W = weak;                                                                     VW = very weak.                                                               Relative intensities are on a scale of 1 to 10.                               *Peaks that occurred in mixtures both before and after hydration are          indicated with an asterisk.                                              

Referring now to Table V-a and Table V-b, therein are shown the infrareddata for a mixture of a propenoate-propenamide polymer, citric acid, andiron sulfate, either unhydrated or previously hydrated and dried.Slight, but significant differences are noted between the absorptionspectra for the unhydrated mixture (Table V-a) and for the hydrated anddried mixture (Table V-b). Fifteen absorption peaks were identified inthe unhydrated mixture versus 19 peaks in the dried gel. There were 12absorption peaks common to both spectra (peak matches). An obviousincrease in the relative intensity/resolution of peak numbers 8 and 19of the dried gel (corresponding to peak numbers 7 and 16, respectively,of the unhydrated material) and the splitting of peak number 11 in TableV-a into two sharply resolved peaks (numbers 12 and 13) in Table V-bwere the major differences noted in the spectrum of the dried gelmaterial.

                  TABLE V-a                                                       ______________________________________                                        Infrared Aosorption Bands Frequency (cm.sup.-1) for a Composite               Mixture of DGP (Iron Sulfate, a Propenoate-Propenamide Polymer,               and Citric Acid) Before Hydration and Drying                                  Peak    Peak         Peak     Relative                                        No.     Position     Intensity                                                                              Intensity                                       ______________________________________                                        *1      3450         S-B      7                                               2       2935         Sh       4                                               *3      2619         Sh       3                                               *4      2087         Sh       2                                               *5      1726         M-Sp     4                                               6       1637         M-B      3                                               *7      1400         VW-Sp    2                                               *8      1385         VW-Sp    2                                               *9      1344         Sh       2                                               *10     1227         W-Sp     2                                                       1122         W-Sp     2                                               *11     982          VW-Sp    1                                               *12     937          VW-Sp    1                                               *13     887          Sh       1                                               *14     791          Sh       1                                               *15     619          W-Sp     2                                               ______________________________________                                         Sh = shoulder;                                                                B = broad;                                                                    Sp = sharp;                                                                   S = strong;                                                                   MS = medium strong;                                                           M = medium;                                                                   W = weak;                                                                     VW = very weak.                                                               Relative intensities are on a scale of 1 to 10.                               *Peaks that occurred in mixtures both before and after hydration are          indicated with an asterisk.                                              

                  TABLE V-b                                                       ______________________________________                                        Infrared Absorption Bands Frequency (cm.sup.-1) for a Composite               Mixture of DGP (Iron Sulfate, a Propenoate-Propenamide Polymer,               and Citric Acid) After Hydration and Drying                                   Peak    Peak         Peak     Relative                                        No.     Position     Intensity                                                                              Intensity                                       ______________________________________                                        *1      3454         S-B      6                                               2       3225         Sh       5                                               *3      2949         Sh       3                                               *4      2640         Sh       2                                               *5      2077         Sh       1                                               *6      1722         Ms-Sp    4                                               7       1660         M-Sp     3                                               *8      1398         W-Sp     2                                               *9      1387         Sh       2                                               *10     1331         Sh       1                                               *11     1227         W-Sp     2                                               12      1130         W-Sp     2                                               13      1115         W-Sp     2                                               *14     982          VW-Sp    0                                               *15     937          VW-Sp    0                                               *16     897          Sh       0                                               17      850          Sh       0                                               *18     793          Sh       1                                               *19     619          W-Sp     2                                               ______________________________________                                         Sh = shoulder;                                                                B = broad;                                                                    Sp = sharp;                                                                   S = strong;                                                                   MS = medium strong;                                                           M = medium;                                                                   W = weak;                                                                     VW = very weak.                                                               Relative intensities are on a scale of 1 to 10.                               *Peaks that occurred in mixtures both before and after hydration are          indicated with an asterisk.                                              

From the discussion of the infrared absorption data, supra, it shouldnow be abundantly clear that changes occurred in the polymer-citricacid-iron sulfate mixtures after hydration and drying which resulted inthe formation of compounds not present in the original mixture, and thatthese compounds represent new compositions of matter.

EXAMPLES

In order that those skilled in the art may better understand how thepresent invention can be practiced, the following examples are given byway of illustration only and not necessarily by way of limitation, sincenumerous variations thereof will occur and will undoubtedly be made bythose skilled in the art without substantially departing from the trueand intended scope and spirit of the instant invention herein taught anddisclosed.

Greenhouse pot experiments were conducted to determine availability ofiron from various commercially available iron sources and DGP, said DGPmixture being formulated with different chemical classes of polymers,with each iron source or DGP mixture being applied in a band (1/4 to 3/4inch in diameter and 4 to 6 inches long at a depth of 2 inches below thesoil surface and 1 inch away from the seed row to a calcareousiron-deficient soil at an application rate ranging between about 10 andabout 40 pounds of iron per acre. For comparison purposes, each ironfertilizer, namely, iron (ferrous or ferric) sulfate and FeEDDHA wasband applied by itself at the same soil depth and distance from the seedrow. In addition, a polyacrylamide polymer formulation of DGP wasfield-tested to determine the effectiveness of the DGP for the ironnutrition of corn growing under actual field conditions.

In the following three examples, unless otherwise indicated, all partsand percentage compositions are by weight. In the greenhouse studies,each pot was 6 inches in diameter and was charged with about 1 kilogramof Epping silt loam soil. The soil in all greenhouse pots was fertilizeduniformly with all known plant nutrients except iron at rates known toprovide optimum plant response, so that any crop responses could beattributed to iron contained in the various materials, including the DGPmixtures, or iron source materials or FeEDDHA or hydrophilicpolymer-iron source materials applied as comparisons to the DGP mixture.See Konrad Mengel, and E. A. Kirkby, Principles of Plant Nutrition,International Potash Institute, Bern, Switzerland (1982), hereinincorporated by reference thereto, for an example of the variety andconcentrations of micronutrients used to satisfy such requirements. Thetest crop for the greenhouse experiments was grain sorghum (Sorghumbicolor L. Moench), cultivar RS-626, a variety known to be susceptibleto iron chlorosis when grown on iron-deficient soils such as the Eppingsilt loam type herein used. Three replicates of each treatment were usedin a completely randomized design. Deionized water was used during theentire growth period and forage was harvested after 6 weeks' growth. Thesoil in greenhouse pots was sliced longitudinally post-harvest toexamine fertilizer band characteristics. In the field study, the DGPwere tested as an iron source for corn (Zea mays L.) in a factorialdesign against other iron source materials using four replications plusan untreated check on high pH Cozad silt loam soil in the State ofNebraska.

The resulting DGP mixtures, containing a proper diet of required iron,have now been found to act to more effectively deliver to the plantstreated therewith the nutrient contained therein. It is believed thatthese products act to focus the beneficial effects of such thereincontained iron due to the fact that proper placement thereof at the soilsitus juxtaposed the plant root both provide a protective matrix foriron contained therein and effectively causes or enhances rootdevelopment and growth to and throughout the regions of soil displacedby "islands" or "veins" of such mixtures while at the same timesupplying a zone of iron outside the DGP band in such form that it isreadily available and accessible to plants, and iron uptake, and thusplant growth, is considerably enhanced.

Accordingly, a first series of tests, reported in Example I, below, wasdesigned to test the response of grain sorghum to iron contained in theDGP mixtures, iron contained in hydrophilic polymer delivery systems,iron contained in FeEDDHA, and iron contained in iron sulfates. Theapplication rates for iron were 18 and 24 mg of iron per kilogram of potsoil for all materials tested. The hydrophilic delivery systems were thesame as those described in the preferred embodiments of Mortvedt, supra.

A second series of tests, reported in Example II, below, was designed totest the response of grain sorghum to iron contained in the DGP mixturesformulated with different chemical classes of hydrophilic polymer, theresponse to iron contained in hydrophilic polymer delivery systems whichcontained either no citric acid or which contained reagent grade citricacid, and the response to FeEDDHA and iron sulfate. The application ratefor all iron source materials tested was 18 mg of iron per kilogram ofpot soil.

A third series of tests, reported in Example III, below, was designed totest the response of corn growing in the field environment to ironcontained in a DGP mixture formulated with a polyacrylamide polymer, oriron contained in iron sulfate, or iron contained in an ironsulfate/elemental sulfur/citrate/iron-lignosulfonate mixture, or ironcontained in two foliar spray applications of 1.5 percent iron sulfateas FeSO₄. In this example, the application rate of iron varied with eachiron-source treatment.

In all series of tests, projected results correlate with the hypothesisthat such DGP product and application procedure will very effectivelyact to enhance plant growth and improve iron nutrition. In addition,results correlate with the hypothesis that such procedure will veryeffectively act to focus plant root growth in the specific regions andareas of iron placement. Finally, such procedure will thereby provide anew, improved, economical, and highly efficient, delivery system foriron to preselected plants or plant pots.

Example I

In the tests comprising this example, iron sulfate, in the reducedstate, was band applied according to the procedures outlined above to acalcareous iron-deficient soil of the type Epping silt loam either aloneor in combination with the DGP mixture containing a polyacrylamidepolymer, or in combination with hydrophilic polymer gels of varyingchemical structure, to wit, a polyacrylamide, or a polyacrylamide pluspolyacrylate. The procedure used to prepare the gels comprising thepolymer and iron sulfate combination was as described in the descriptionof the preferred embodiments in Mortvedt, supra. The resulting materialswere subsurface band applied to soil forming about 1/4 inch diameterbands onto the soil in the test pots. The synthetic chelate, FeEDDHA,also was similarly band applied alone to soil. All iron source materialswere applied at two different rates, i.e., at 18 and at 24 mg of ironper kilogram of pot soil. It should be noted that in the test comprisingthis Example I, described in detail infra, typical 6-inch(150-millimeter) diameter greenhouse pots were used, with each 6-inchpot containing, on the average, 1 kilogram of iron-deficient soil. Also,typical to iron response tests, the potted crop was sorghum since it haslong been used as a standard for such types of testing with 6 plantsbeing maintained in each pot. See, for example, Aubra Mathers, Effect offerrous sulfate and sulfuric acid on grain sorghum yields, Agron. J.62:555-556 (1970). Typically, after six weeks' of growth in thegreenhouse environment the above-ground plant forage was harvested,dried, and weighed to determine response to testing materials relativeto sorghum grown in pots as standards. Post-harvest examination of thebands was made by slicing the soil longitudinally along the fertilizerband. Visual observations for treatment effects, as judged by the degreeof chlorosis in plants, indicated that there were no differences ineffectiveness between the DGP and FeEDDHA. However, sorghum forageyields and uptake of iron were highest with the DGP mixture, see TableVI, infra; the synthetic chelate FeEDDHA which was previously known tobe the most effective iron fertilizer, ranked second below the DGP inyields and iron uptake. The hydrophilic polymer delivery system ofMortvedt, supra, ranked third. Crop response was lower still with FeSO₄band applied alone. Post-harvest examination of soil showedwell-hydrated, or gelled, bands of DGP into which roots had freelypenetrated and proliferated. In addition, plant roots tended to beconcentrated in the DGP band, and in an orange-colored diffusion zonearound the DGP band, rather than evenly distributed throughout the plantgrowth media, i.e., an enhanced root growth region.

                                      TABLE VI                                    __________________________________________________________________________                      Fe band applied to soil (mg/pot)                            Test                                                                             Source/Wt. %                                                                         Source/Wt. % of                                                                       Chlorisis.sup.2                                                                     Yield, g/pot                                                                          Fe uptake, mg/pot                             No.                                                                              of Fe  Polymer.sup.1                                                                         0 18                                                                              24                                                                              0 18 24 0  18 24                                      __________________________________________________________________________    1  DGP.sup.3                                                                            A       --                                                                              A A --                                                                              47.2                                                                             48.3                                                                             -- 3.22                                                                             3.45                                       (1.0)  (10)                                                                2  Hydro- A       --                                                                              B B --                                                                              32.0                                                                             34.0                                                                             -- 2.53                                                                             2.54                                       gel.sup.4                                                                            (4.5)                                                                  (0.12)                                                                     3  Hydro- B       --                                                                              B B --                                                                              27.0                                                                             28.1                                                                             -- 2.02                                                                             2.29                                       gel    (4.5)                                                                  (0.12)                                                                     4  FeEDDHA                                                                              --      --                                                                              A A --                                                                              42.7                                                                             49.1                                                                             -- 2.83                                                                             2.39                                       (100)  (0)                                                                 5  FeSO.sub.4                                                                           --      --                                                                              D D --                                                                              17.2                                                                             17.7                                                                             -- 0.73                                                                             0.78                                       (100)  (0)                                                                 6  Control                                                                              --      D --                                                                              --                                                                              3.8                                                                             -- -- 0.27                                                                             -- --                                         (0)    (0)                                                                 __________________________________________________________________________     .sup.1 Apolyacrylamide; Bcommercial polyacrylamide and polyacrylate           mixture (50% w/w).                                                            .sup.2 Chlorosis rating scale: A = none; B = slight; C = moderate; D =        severe.                                                                       .sup.3 DGP  dried gel particles consist of 7% polymer, 10% citric acid, 5     FeSO.sub.4 to give an iron concentration of 1.0%).                            .sup.4 Hydrogel  fluid gel formulated to Mortvedt, supra.                

Example II

In the tests comprising this example, the DGP, formulated with (Test No.1, Table VI, supra) or without citric acid, and a polyacrylamidepolymer, and four other different chemical classes of polymer(polyacrylamide/polyacrylate, cellulose ether, guar gum, andpropenoate-propenamide) which contained citric acid, were comparedagainst hydrophilic polymer delivery systems of Mortvedt, supra, whicheither contained or did not contain (Table VII, infra, Test No. 3 and 4)citric acid, for effectiveness as iron sources for grain sorghum. Thesame fertilizing, planting, and cropping procedures used in Example I,above, were followed in these tests. Both FeSO₄ and FeEDDHA were eachband applied alone to soil and all iron sources were applied at a rateof 18 mg of iron per pot. As in Example I, supra, in this and subsequentexamples, the reference to band application is understood to mean theprocedure set forth in the introductory portion of this section. Cropresponse to the iron sources was greatest with the DGP formulated with apolyacrylamide polymer plus citric acid. The FeEDDHA treatment rankedsecond, and the hydrophilic delivery system of Mortvedt, supra,consisting of polyacrylamide and iron sulfate to which citric acid wasadded (Test No. 3) ranked third. Crop response was poorest with FeSO₄alone. Although the DGP containing the propenoate-propenamide polymer(Test No. 9, infra) did not produce as satisfactory results as the otherDGP, and it ranked below FeEDDHA and Test No. 3 in effectiveness, itnonetheless prevented iron chlorosis in the plants and is still lesscostly than the chelate. The same qualities of root penetration andproliferation as shown in Example I, supra, were again evident with allthe DGP, although only the DGP containing the polyacrylamide and thecellulose ether manifested the orange-colored diffusion zone, supra. Theranking of the products in this test according to yields and iron uptakeof plants is presented in Table VII, infra, wherein there is clearlydemonstrated the superior attributes of the instant invention in thisexample and, further wherein is clearly shown that citric acid is anessential component of such systems, without which plant vigor and ironnutrition is much reduced.

                  TABLE VII                                                       ______________________________________                                                                Citric                                                                             Fe band                                               Source/   Source/  acid applied to soil (18 mg/pot)                      Test Wt. %     Wt.% of  Wt.  Chlorosis                                                                            Yield,                                                                              Fe uptake,                          No.  of Fe     Polymer.sup.1                                                                          %    rating g/pot mg/pot                              ______________________________________                                        1    DGP.sup.3 A        10.0 A      41.1  2.27                                     (1.0)     (7)                                                            2    DGP       A        --   D      13.2  0.37                                     (1.0)     (7)                                                            3    Hydro-    A         5.0 A      35.0  1.83                                     gel.sup.4 (4.5)                                                               (0.12)                                                                   4    Hydro-    A        --   B      30.2  1.29                                     gel       (4.5)                                                               (0.12)                                                                   5    Hydro-    B         5.0  B+    28.1  1.59                                     gel       (4.5)                                                               (0.12                                                                    6    Hydro-    B        --   C      20.7  1.01                                     gel       (4.5)                                                               (0.12                                                                    7    DGP       C        10.0 A      33.0  2.06                                     (1.0)     (7)                                                            8    DGP       D        10.0 A      32.9  2.11                                     (1.0)     (7)                                                            9    DGP       E        10.0 A      27.1  1.60                                     (1.0)     (10)                                                           10   FeEDDHA   --       --   A      39.1  1.83                                     (100)     (0)                                                            11   FeSO.sub.4                                                                              --       --   D      11.4  0.45                                     (100)     (0)                                                            12   Control   --       --   D      6.2   0.46                                     (0)       (0)                                                            ______________________________________                                         .sup.1 Apolyacrylamide; Bcommercial polyacrylamide and polyacrylate           mixture (50% w/w); Ccellulose ether; Dguar gum; Epropenoate-propenamide.      .sup.2 Chlorosis rating scale: A = none; B = slight; C = moderate; D =        severe.                                                                       .sup.3 DGP  dried gel particles consist of 7% polymer, 10% citric acid, 5     FeSO.sub.4 (to give an iron concentration of 1.0%)                            .sup.4 Hydrogel  fluid gel formulated to Mortvedt, supra. The citric acid     concentration of 5% was the maximum that could be absorbed in these gels.     On a dry weight basis, the concentrations of iron, polymer, and citric        acid are 9.63%, 90.4%, and 25%, respectively.                            

Example III

A third series of tests, reported below, was designed to test theresponse of corn to a polyacrylamide plus citric acid formulation of DGPin a field environment. The experiment was a factorial design using twocorn varieties (tolerant and non-tolerant to high soil pH, designated asP3362 and P3398, respectively, in Table VIII, below) and five irontreatments applied in the seed furrow, plus an untreated check. Fourreplications of each treatment and of the untreated check were used. Theexperiment was established in Nebraska on three areas of Cozad silt loamsoil that ranged in pH from slightly above neutral (pH 7.7) tocalcareous (pH 8.6). Plot size was four individual rows 15 feet longwith 30 inch spacing between rows. Iron source treatments consisted ofDGP applied at 5 and 10 pounds of iron per acre (designated as DGP1 andDGP2 in Table VIII, below), iron sulfate applied at 50 pounds per acre(designated as FeSO₄ in Table VIII), an iron sulfate/elementalsulfur/citrate/iron-lignosulfonate mixture (designated as FeMIX in TableVIII) applied at 90 pounds per acre, or two foliar spray applications of1.5 percent iron sulfate as FeSO₄ (designated as FOLIAR in Table VIII).Measures of treatment effectiveness were plant height, the chlorophyllcontent of leaves (since iron is essential for chlorophyll formation),and yields of corn grain reported as bushels per acre. An increase inplant height and in the leaf chlorophyll content are at least strongindicators of increased plant vigor, while an increase in yield is thefinal definitive measure of product effectiveness. The effectiveness ofthe DGP as an iron source in calcareous soil (site 1) is clearly shownin Table VIII, where plant height and leaf chlorophyll content (bothmeasured 80 days after planting), and final grain yields aresignificantly greater with the DGP applications than with the other ironsource treatments. Moreover, the DGP treatments resulted significantimprovement in the three measured parameters for the crop variety whichhas been developed to be less susceptible to iron deficiency, which wasan even stronger indication of the efficacy of the DGP materials. Inaddition, photographic documentation, commencing at an early stage ofplant growth and development (14 days) and continuing until plantsenesence and harvest of grain (120 days) clearly showed the dramaticdifferences in the plant height and green color of plants treated withDGP and further substantiated the actual measurements shown in TableVIII. As pointed out in the description of the prior art, supra, irondeficiency occurs most frequently in calcareous, high pH soils, andchlorosis occurs most usually in plants grown therein, but usually withdecreasing occurrence and severity as soils tend towards a neutral pH.Correction of chlorosis is also the most difficult in such soils, and ingeneral, tends to be more easily corrected as soils tend toward aneutral pH if, indeed, the problem occurs at all. The vigor and yieldsof the plants grown on Site 2 and Site 3 support this contention, whilethe increase in plant vigor and yields on Site 1 demonstrate theefficacy of the DGP product.

The exact location of the original test plots was mapped at the end ofthe growing season. A corn crop was then planted one year later in theplots to test for residual effects of the DGP treatments. No additionalDGP or other iron source was applied at planting. Photographicdocumentation clearly showed a response to the original DGP application,as evidenced by a marked increase in plant vigor (plant height, growthrate, and absence of chlorosis) over plants growing in other areas ofthe test plots. This response was evident throughout the entire growingseason. The plants growing in plots which had received other treatmentslisted in Table VIII, supra, the previous year were stunted andchlorotic. This clearly indicates the long-term efficacy of the DGP, andsupports the economic viability of the DGP since yearly applications maybe unnecessary.

                                      TABLE VIII                                  __________________________________________________________________________           Iron Plant Height                                                                           Chlorophyll Meter                                                                      Yield, bu/A                                     Test   Treat-                                                                             Site.sup.3                                                                             Site     Site                                            Mp Variety.sup.1                                                                     ment.sup.2                                                                         1  2  3  1  2  3  1  2  3                                         __________________________________________________________________________    1  P3362                                                                             Check                                                                              14.8                                                                             21.8                                                                             28.3                                                                             12.3                                                                             52.1                                                                             53.4                                                                              44                                                                              174                                                                              181                                       2      FOLIAR                                                                             17.0                                                                             22.8                                                                             26.5                                                                             25.1                                                                             53.1                                                                             55.5                                                                              80                                                                              180                                                                              195                                       3      FeSO.sub.4                                                                         19.5                                                                             23.3                                                                             29.5                                                                             32.9                                                                             54.5                                                                             55.9                                                                              98                                                                              181                                                                              199                                       4      FEMIX                                                                              20.3                                                                             25.0                                                                             28.3                                                                             27.1                                                                             53.3                                                                             54.1                                                                             102                                                                              185                                                                              186                                       5      DGP1 22.8                                                                             24.5                                                                             28.3                                                                             46.8                                                                             51.5                                                                             54.8                                                                             133                                                                              176                                                                              198                                       6      DGP2 22.3                                                                             24.8                                                                             29.3                                                                             47.9                                                                             55.5                                                                             56.0                                                                             131                                                                              182                                                                              188                                       7  P3398                                                                             Check                                                                              6.3                                                                              20.8                                                                             25.0                                                                             4.4                                                                              49.1                                                                             51.1                                                                              1 164                                                                              179                                       8      FOLIAR                                                                             8.0                                                                              22.0                                                                             24.3                                                                             14.5                                                                             47.3                                                                             51.9                                                                              6 174                                                                              176                                       9      FeSO.sub.4                                                                         17.5                                                                             23.0                                                                             24.8                                                                             12.3                                                                             49.4                                                                             50.5                                                                              26                                                                              170                                                                              182                                       10     FEMIX                                                                              19.5                                                                             22.0                                                                             27.0                                                                             20.9                                                                             51.4                                                                             52.5                                                                              44                                                                              178                                                                              182                                       11     DGP1 23.8                                                                             24.8                                                                             26.2                                                                             45.7                                                                             52.2                                                                             53.6                                                                             102                                                                              173                                                                              183                                       12     DGP2 24.3                                                                             24.0                                                                             26.0                                                                             51.3                                                                             51.6                                                                             52.8                                                                             110                                                                              178                                                                              184                                       __________________________________________________________________________     .sup.1 Variety P3362 is a Pioneer, high pHiron deficiency tolerant            variety; Variety P3398 is a Pioneer, high pHiron deficiency susceptible       variety.                                                                      .sup.2 Check  no applied iron; FOLIAR  two foliar spray applications of       1.5% iron sulfate; FeSO.sub.4  iron sulfate applied at 50 lb/A; FEMIX         iron sulfate/elemental sulfur/citrate/ironlignosulfonate mixture applied      at 90 lb/A; DGPdried gel particles contain 7.0% polyacrylamide, 10.0%         citric acid, and 5.0% FeSO.sub.4 (to give an iron concentration of 1.0%).     DGP1  applied at 5 lb Fe/A; DGP2  applied at 10 lb Fe/A.                      .sup.3 Site 1: Calcareous  pH 8.6; Site 2: Slightly calcareous  pH 8.2;       Site 3: Near neutral  pH 7.7.                                            

INVENTION PARAMETERS

After sifting and winnowing through the data herein presented, as wellas other results and operations of our new, novel, and improvedtechnique, including methods and means for the effecting thereof, theoperating variables, including the acceptable and preferred conditionsfor carrying out our invention are summarized below:

    ______________________________________                                                                          Most                                                      Operating Preferred Preferred                                   Variables     Limits.sup.1                                                                            Limits.sup.1                                                                            Limits.sup.1                                ______________________________________                                        Polymer.sup.2 1-15%     5-15%     7%                                                        (14-60)   (30-38)   (32)                                        Iron Sulfate  1-15%     3-10%     5%                                                        (14-30)   (20-25)   (23)                                        Citric Acid   5-20%     5-15%     10%                                                       (0.7-50)  (38-50)   (45)                                        Water         ≦93%                                                                             ≦87%                                                                             78%                                         Film Thickness of                                                                           1/8"-1/2" 1/4"-1/2" 1/4"                                        Undried Hydrogel                                                              Drying Temperature                                                                          90-120    100-110   105                                         (°C.)                                                                  Time of Effective                                                                           4-20      10-16     10                                          Drying (h)                                                                    ______________________________________                                         .sup.1 Concentrations of polymer, iron sulfate, and citric acid, on a         weight basis, in formulations on a per kilogram basis after mixing with       deionized water, but before drying. Approximate concentrations after          drying shown in parenthesis. Final concentrations of ingredients on a dry     weight basis may total less than 100% due to water loss during drying. Th     solvation capacity of a given polymer often limits the amounts of soluble     salts (i.e., sulfates and/or citrates) contained in the final, dried          product.                                                                      .sup.2 Crosslinked polyacrylamide, polyacrylate, guar gum, cellulose          ether, or propenoatepropenamide, preferably from about 1 to about 5%          crosslinking, and most preferably from about 1 to about 3% crosslinking       (above about 10% crosslinking could result in a plastic or solid material     before drying, with insufficient absorption of iron and citric acid), or      natural guar polymer with no crosslinking.                               

While we have shown and described particular embodiments of ourinvention, modifications and variations thereof will occur to thoseskilled in the art. We wish it to be understood therefore that theappended claims are intended to cover such modifications and variationswhich are within the true scope and spirit of our invention.

What we claim as new and desire to secure by Letters of Patent of theUnited States is:
 1. A composition of matter comprising dried particlesof iron-containing hydrophilic gel, said gel containing from about 14percent to about 60 percent by weight of a hydrophilic polymercomprising polyacrylamide; from about 1 percent to about 50 percent byweight of hydroxy acid; and from about 14 percent to about 30 percent byweight of iron sulfate, said composition further characterized by thefollowing tabulation of peak numbers, peak positions, peak intensities,and relative intensities of infrared absorption band frequency (cm⁻¹):

    ______________________________________                                        Peak No.                                                                              Peak Position                                                                             Peak Intensity                                                                            Relative Intensity                            ______________________________________                                        1       3481        MS-Sp       4                                             2       3400        MS-Sp       4                                             3       3215        MS-B        4                                             4       2937        Sh          3                                             5       2700        Sh          2                                             *6      2621        W-B         2                                             7       2540        W-B         2                                             *8      1730        S-Sp        5                                             9       1659        Ms-Sp       4                                             10      1610        S-Sp        4                                             11      1566        Sh          4                                             12      1419        Ms-Sp       4                                             *13     1396        S-Sp        4                                             14      1377        Sh          4                                             15      1325        MS-Sp       3                                             16      1286        Ms-Sp       3                                             *17     1225        Ms-Sp       4                                             18      1194        MS-Sp       4                                             19      1142        S-Sp        4                                             *20     1109        S-Sp        4                                             21      1074        MS-Sp       4                                             *22     978         Sh          3                                             *23     937         W-Sp        2                                             *24     891         M-Sp        3                                             25      850         M-Sp        3                                             *26     795         M-Sp        3                                             *27     613         Ms-Sp       4                                             28      580         Ms-Sp       4                                             29      540         Sh          4                                             ______________________________________                                    

wherein Sh=shoulder; B=broad; Sp=sharp; S=strong; MS=medium strong;M=medium; W=weak; VW=very weak: wherein the relative intensities are ona scale of 1 to 10 and peaks that occurred in mixtures both before andafter hydration are indicated with an asterisk (*).
 2. A composition ofmatter comprising dried particles of iron-containing hydrophilic gel,said gel containing from about 14 percent to about 60 percent by weightof a hydrophilic polymer comprising guar gum; from about 1 to about 50percent to about 50 percent by weight of hydroxy acid; and from about 14percent to about 30 percent by weight of iron sulfate, said compositionfurther characterized by the following tabulation of peak numbers, peakpositions, peak intensities, and relative intensities of infraredabsorption band frequency (cm⁻¹):

    ______________________________________                                        Peak No. Peak Position                                                                             Peak Intensity                                                                            Relative Intensity                           ______________________________________                                        1        3388        S-B         8                                            *2       2941        Sh          5                                            3        2629        W-B         2                                            *4       1992        VW-B        1                                            5        1732        S-Sp        8                                            *6       1633        W-Sp        2                                            7        1400        M-Sp        4                                            8        1194        S-Sp        7                                            9        1138        Ms-Sp       6                                            *10      1082        MS-Sp       6                                            11       1018        Sh          4                                            12       976         Sh          2                                            *13      941         Sh          2                                            *14      897         VW-Sp       2                                            *15      874         VW-Sp       2                                            16       812         W-Sp        3                                            17       665         W-Sp        2                                            18       623         W-Sp        3                                            *18      602         W-Sp        3                                            19       525         W-Sp        3                                            ______________________________________                                    

wherein Sh=shoulder; B=broad; Sp=sharp; S=strong; MS=medium strong;M=medium; W=weak; VW=very weak: wherein the relative intensities are ona scale of 1 to 10 and peaks that occurred in mixtures both before andafter hydration are indicated with an asterisk (*).
 3. A composition ofmatter comprising dried particles of iron-containing hydrophilic gel,said gel containing from about 14 percent to about 60 percent by weightof a hydrophilic polymer comprising polyacrylate; from about 1 percentto about 50 percent by weight of hydroxy acid; and from about 14 percentto about 30 percent by weight of iron sulfate, said composition furthercharacterized by the following tabulation of peak numbers, peakintensities, and relative intensities of infrared absorption bandfrequency (cm⁻¹):

    ______________________________________                                        Peak No. Peak Position                                                                             Peak Intensity                                                                            Relative Intensity                           ______________________________________                                        1        3479        MS-Sp       7                                            2        3398        S-Sp        8                                            3        3242        Sh          6                                            4        2976        Sh          5                                            *5       2619        W-Bp        3                                            6        2542        Sh          3                                            *7       1981        Vw-B        1                                            *8       1728        S-Sp        9                                            *9       1610        M-Sp        6                                            10       1564        W-Sp        4                                            11       1554        W-Sp        4                                            12       1502        Sh          2                                            13       1479        Sh          2                                            14       1419        M-Sp        5                                            *15      1396        M-Sp        5                                            16       1375        Sh          4                                            17       1325        W-Sp        4                                            18       1286        M-Sp        4                                            *19      1230        M-Sp        5                                            20       1194        M-Sp        5                                            *21      1144        M-Sp        6                                            *22      1103        M-Sp        6                                            23       1072        M-Sp        4                                            *24      982         VW-Sp       2                                            *25      939         VW-Sp       2                                            *26      893         VW-Sp       2                                            *27      876         Sh          2                                            28       850         VW-Sp       2                                            29       795         W-Sp        3                                            30       700         Sh          3                                            31       669         Sh          3                                            32       617         W-Sp        4                                            33       580         W-Sp        4                                            34       563         Sh          4                                            35       540         W-Sp        4                                            ______________________________________                                    

wherein Sh=shoulder; B=broad; Sp=sharp; S=strong; MS=medium strong;M=medium; W=weak; VW=very weak: wherein the relative intensities are ona scale of 1 to 10 and peaks that occurred in mixtures both before andafter hydration are indicated with an asterisk (*).
 4. A composition ofmatter comprising dried particles of iron-containing hydrophilic gel,said gel containing from about 14 percent to about 60 percent by weightof a hydrophilic polymer comprising cellulose ether; from about 1percent to about 50 percent by weight of hydroxy acid; and from about 14percent to about 30 percent by weight of iron sulfate, said compositionfurther characterized by the following tabulation of peak numbers, peakpositions, peak intensities, and relative intensities of infraredabsorption band frequency (cm⁻¹):

    ______________________________________                                        Peak No. Peak Position                                                                             Peak Intensity                                                                            Relative Intensity                           ______________________________________                                        *1       3423        S-B         7                                            *2       2941        M-B         4                                            *3       2621        VW-B        2                                            *4       2010        VW-B        1                                            *5       1728        S-Sp        7                                            *6       1632        W-Sp        3                                            *7       1390        W-Sp        3                                            *8       1350        W-Sp        3                                            9        1298        W-Sp        3                                            10       1205        MS-Sp       6                                            11       1126        MS-Sp       5                                            12       1078        MS-Sp       5                                            *13      945         Sh          2                                            *14      883         VW-B        1                                            *15      796         W-B         2                                            *16      602         M-Sp        3                                            17       523         Sh          3                                            ______________________________________                                    

wherein Sh=shoulder; B=broad; Sp=sharp; S=strong; MS=medium strong;M=medium; W=weak; VW=very weak: wherein the relative intensities are ona scale of 1 to 10 and peaks that occurred in mixtures both before andafter hydration are indicated with an asterisk (*).
 5. A composition ofmatter comprising dried particles of iron-containing hydrophilic gel,said gel containing from about 14 percent to about 60 percent by weightof a hydrophilic polymer comprising propenoate-propenamide; from about 1percent to about 50 percent by weight of hydroxy acid; and from about 14percent to about 30 percent by weight of iron sulfate, said compositionfurther characterized by the following tabulation of peak numbers, peakpositions, peak intensities, and relative intensities of infraredabsorption band frequency (cm⁻¹):

    ______________________________________                                        Peak No  Peak Position                                                                             Peak Intensity                                                                            Relative Intensity                           ______________________________________                                        *1       3454        S-B         6                                            2        3225        Sh          5                                            *3       2949        Sh          3                                            *4       2640        Sh          2                                            *5       2077        Sh          1                                            *6       1722        Ms-Sp       4                                            7        1660        M-Sp        3                                            *8       1398        W-Sp        2                                            *9       1387        Sh          2                                            *10      1331        Sh          1                                            *11      1227        W-Sp        2                                            12       1130        W-Sp        2                                            13       1115        W-Sp        2                                            *14      982         VW-Sp       0                                            *15      937         VW-Sp       0                                            *16      897         Sh          0                                            17       850         Sh          0                                            *18      793         Sh          1                                            *19      619         W-Sp        2                                            ______________________________________                                    

wherein Sh=shoulder; B=broad; Sp=sharp; S=strong; MS=medium strong;M=medium; W=weak; VW=very weak: wherein the relative intensities are ona scale of 1 to 10 and peaks that occurred in mixtures both before andafter hydration are indicated with an asterisk (*).